Video encoding devices for encoding moving images to generate encoded data, and video decoding devices for decoding the encoded data to generate decoded images are used for efficient transmission or recording of moving images.
Specifically, video coding standards are available, such as H.264/MPEG-4.AVC, the standard implemented in KTA software, which is a codec for joint development in VCEG (Video Coding Expert Group), the standard implemented in TMuC (Test Model under Consideration) software, and the standard proposed in HEVC (High-Efficiency Video Coding), which is a codec successor to H.264/MPEG-4.AVC (NPLs 1 and 4).
In such video coding standards, images (pictures) forming a moving image are managed using a hierarchical structure that is composed of slices obtained by partitioning each image, coding units obtained by splitting each slice, and blocks and partitions obtained by splitting each coding unit. The images (pictures) are generally encoded/decoded on a block-by-block basis.
In such video coding standards, generally, a prediction image is generated based on a locally decoded image obtained by encoding/decoding an input image, and the prediction image is subtracted from the input image (original image) to obtain a prediction residual (also referred to as a “differential image” or a “residual image”) which is then encoded. Methods of generating prediction images include inter-frame prediction (inter prediction) and intra-frame prediction (intra prediction).
In intra prediction, a prediction image in a frame is sequentially generated based on a locally decoded image in this frame.
In inter prediction, on the other hand, a prediction image in a frame to be predicted is generated in units of prediction units (for example, blocks) by applying motion compensation using motion vectors to a reference image in a reference frame (decoded image) the entirety of which has been decoded.
As for inter prediction, a technique of splitting a coding unit, which is the unit of a coding process, into asymmetric partitions (PUs) when using inter prediction was adopted (AMP; Asymmetric Motion Partition, NPLs 2 and 3) at the sixth meeting of the JCT-VC, which was recently held (Torino, IT, 14-22 Jul., 2011).
It has also been proposed that non-square quadtree transform (NSQT) be used if the type of partition is an asymmetric partition (NPL 2).